Led by Rube Foster, owner and manager of the Chicago American Giants, the NNL was established on February 13, 1920 by a coalition of team owners at a meeting in a Kansas City YMCA.[1] The new league was the first African-American baseball circuit to achieve stability and last more than one season. At first the league operated mainly in midwestern cities, ranging from Kansas City in the west to Pittsburgh in the east; in 1924 it expanded into the south, adding franchises in Birmingham and Memphis.

The NNL survived controversies over umpiring, scheduling, and what some perceived as league president Rube Foster's disproportionate influence and favoritism toward his own team. It also outlasted Foster's decline into mental illness in 1926, and its eastern rival, the ECL, which folded in early 1928. The NNL finally fell apart in 1931 under the economic stress of the Great Depression.

The Negro American League, founded in 1937 and including several of the same teams that played in the original Negro National League, would eventually carry on as the western circuit of black baseball. A separate Negro National League was organized in 1933, but eventually became concentrated on the east coast. To distinguish between the two unrelated leagues, they are usually referred to as the first Negro National League (or NNL I) and the second Negro National League (or NNL II).

From 1920 through 1924, the team in first place at the end of the season was declared the Pennant winner. Due to the unorthodox nature of the schedule (and little incentive to enforce it), some teams frequently played many more games than others did in any given season. This led to some disputed championships and two teams claiming the title. Generally, the team with the best winning percentage (with some minimum number of games played) was awarded the Pennant, but other times it was the team with the most victories. The "games behind" method of recording standings was uncommon in most black leagues.

1920 – Chicago American Giants

1921 – Chicago American Giants

1922 – Chicago American Giants

1923 – Kansas City Monarchs

1924 – Kansas City Monarchs‡

1925 – Kansas City Monarchs†‡

1926 – Chicago American Giants†‡

1927 – Chicago American Giants†‡

1928 – St. Louis Stars†

1929 – Kansas City Monarchs†

1930 – St. Louis Stars†

1931 – St. Louis Stars† (season did not finish; Stars had best record among league members and were declared the champions,[2] though non-member Pittsburgh Crawfords disputed title)

† – Pennant was decided via a split-season schedule with the winner of the first half of the season playing the winner of the second half of the season, unless one team won both halves.
‡ – Pennant winner went on to play in the Colored World Series.

From 1925 through 1931, the NNL split the season into two halves. The winner of the first half played the winner of the second half for the league Pennant. As mentioned above, disputes also occurred in the split season finishes.

For the duration of the league, a Colored World Series took place four times, from 1924 through 1927. The NNL Pennant winner met the champion of the rival Eastern Colored League. Three out of the four years, the Negro National League team (below in bold) prevailed.